The present invention relates generally to techniques for the manufacture of photovoltaic devices. More particularly, the present invention provides a method and structure for eliminating peeling of a photovoltaic absorber film from the lower conductive material. Merely by way of examples, the present method is implemented within a routine patterning process for the manufacture of thin-film photovoltaic modules to prevent peeling caused by impurity from edge region of the substrate, but it would be recognized that the invention may have other applications.
From the beginning of time, mankind has been challenged to find way of harnessing energy. Energy comes in the forms such as petrochemical, hydroelectric, nuclear, wind, biomass, solar, and more primitive forms such as wood and coal. Over the past century, modern civilization has relied upon petrochemical energy as an important energy source. Petrochemical energy includes gas and oil. Gas includes lighter forms such as butane and propane, commonly used to heat homes and serve as fuel for cooking Gas also includes gasoline, diesel, and jet fuel, commonly used for transportation purposes. Heavier forms of petrochemicals can also be used to heat homes in some places. Unfortunately, the supply of petrochemical fuel is limited and essentially fixed based upon the amount available on the planet Earth. Additionally, as more people use petroleum products in growing amounts, it is rapidly becoming a scarce resource, which will eventually become depleted over time.
More recently, environmentally clean and renewable sources of energy have been desired. An example of a clean source of energy is hydroelectric power. Hydroelectric power is derived from electric generators driven by the flow of water produced by dams such as the Hoover Dam in Nevada. The electric power generated is used to power a large portion of the city of Los Angeles in Calif. Clean and renewable sources of energy also include wind, waves, biomass, and the like. That is, windmills convert wind energy into more useful forms of energy such as electricity. Still other types of clean energy include solar energy. Specific details of solar energy can be found throughout the present background and more particularly below.
Solar energy technology generally converts electromagnetic radiation from the sun to other useful forms of energy. These other forms of energy include thermal energy and electrical power. For electrical power applications, solar cells are often used. Although solar energy is environmentally clean and has been successful to a point, many limitations remain to be resolved before it becomes widely used throughout the world. As an example, one type of solar cell uses crystalline materials, which are derived from semiconductor material ingots. These crystalline materials can be used to fabricate optoelectronic devices that include photovoltaic and photodiode devices that convert electromagnetic radiation into electrical power. However, crystalline materials are often costly and difficult to make on a large scale. Additionally, devices made from such crystalline materials often have low energy conversion efficiencies. Other types of solar cells use “thin film” technology to form a thin film of photosensitive material to be used to convert electromagnetic radiation into electrical power. Similar limitations exist with the use of thin film technology in making solar cells. That is, efficiencies for thin-film photovoltaic cells based on various types of absorber materials are often relatively poor. Recently, many improvements in thin-film material processing have been achieved in the manufacture of high efficiency monolithic integrated thin-film solar modules on large glass substrates. For example, sodium doping is found to enhance the IV characteristics of the copper-indium-selenium based photovoltaic cells. While un-controlled sodium species in the thin-film photovoltaic cells are also found to cause degradation of the films. In particular, excessive sodium species may cause the thin-film absorber being peeled off from the conductive material that serves as bottom electrode, especially from one or more edge regions. These and other limitations of these conventional thin-film solar module manufacture techniques can be found throughout the present specification and can be improved by applying one or more embodiments of present invention described in the specification below.